1. Field of the Invention
The present invention relates to a color liquid crystal display panel which comprises thin film transistors, and more particularly, to a color liquid crystal display panel in which tight contact between a black matrix and an underlying member is improved so as to achieve high fineness.
2. Description of the Related Art
A color liquid crystal display panel comprises two glass substrates and a liquid crystal layer which is disposed between the glass substrates. In general, in a panel of the thin film transistor (TFT; Thin Film Transistor) type, color layers of three colors (red, green and blue) are formed on a counter glass substrate which is faced with a TFT-side glass substrate which seats TFTs. However, since such a structure demands large margins for a black matrix which is disposed between adjacent inter-pixel opening portions to improve contrast, it is difficult to enhance the fineness of the panel with this structure.
Against this background, a color liquid crystal display panel seating three color layers on a TFT-side substrate has attracted attention over recent years. FIG. 1 is a cross sectional view of a conventional color liquid crystal display panel in which three color layers are formed on a TFT-side substrate.
In a conventional color liquid crystal display panel, a liquid crystal layer 117 is disposed between a TFT-side glass substrate 101 and a counter glass substrate 102. In the following, the closer sides to the liquid crystal layer 117 of the glass substrates 101 and 102 will be referred to as xe2x80x9cthe inner sidesxe2x80x9d and the opposite sides will be referred to as xe2x80x9cthe outer sides.xe2x80x9d
Gate electrodes 103 are formed on an inner-side surface of the TFT-Side glass substrate 101, and a gate insulation film 104 is formed so as to cover the gate electrodes 103. The gate electrodes 103 are connected to gate lines (not shown) which extend in the direction of rows in the panel.
A semiconductor layer 105 is formed on an inner-side surface of the gate insulation film 104 at positions corresponding to the respective gate electrodes 103, and drain electrodes 106 and source electrodes 107 are formed so as to sandwich the semiconductor layer 105. The drain electrodes 106 are connected to signal lines (not shown) which extend in the direction of columns. On the other hand, the source electrodes 107 are intrinsic to the respective TFTs 108. In this manner, the plurality of TFTs 108 are arranged in the form of a matrix. Further, an insulation film 109 is formed entirely over the inner-side surface of the TFT-side glass substrate 101 so as to coat the TFTs 108.
A black resin layer (black matrix) 113 is formed on the respective TFTs 108 so as to sandwich the insulation layer 109 with the respective TFTs 108. The black resin layer 113 is formed also on the respective gate lines, the respective signal lines and a frame portion 120 of the panel so as to sandwich the insulation layer 109 with them.
At the inter-pixel opening portions from which the red light is to be emitted, a red layer 110 alone is disposed as a color layer on the insulation layer 109. At the inter-pixel opening portions from which the green light is to be emitted, a green layer 111 alone is disposed as a color layer on the insulation layer 109. At the inter-pixel opening portions from which the blue light is to be emitted, a blue layer (not shown) alone is disposed an a color layer on the insulation layer 109.
Still further disposed entirely on the inner-side surface of the TFT-side glass substrate 101 is a flattened film 114 which has a flattened surface and covers the TFTs 108, the black resin layer 113 and the like. The flattened film 114 includes a plurality of contact holes 118 which reach even to the respective source electrodes 107, and pixel electrodes 115 of an ITO film are formed inside the contact holes 118. The pixel electrodes 115 protrude beyond and extend on the flattened film 114, thereby covering the color layers at the respective inter-pixel opening portions.
Meanwhile, a counter transparent common electrode 116 is formed on the inner-side surface of the counter glass substrate 102 such that the counter transparent common electrode 116 stretches to face the respective pixel electrodes 115. The counter transparent common electrode 116 is formed of an ITO film.
A sealant 119 surrounding the liquid crystal layer 117 is disposed between the glass substrates 101 and 102 In addition, an alignment film (not shown) is formed on each of the flattened film 114 and the counter transparent common electrode 116.
In such a conventional color liquid crystal display panel, since the black matrix 113 is formed on the inner-side surface of the TFT-side glass substrate 101 it is possible to reduce the widths of the black matrix 113. As a result, it is possible to improve an opening ratio beyond that heretofore achievable. For example, an XGA panel can have an opening ratio of about 80%.
In the case of the conventional color liquid crystal display panel as above, in which the three color layers are formed on the TFT-side substrate, during fabrication of the panel, after applying, developing and baking on the respective color layers or before forming the respective color layers, a black resin film which is a raw material of the black matrix is applied, developed and baked. Since the width used under the optimal condition for development (development margin) of the black resin film is extremely narrow, there is a problem in that the black resin film easily falls off the insulation film 109 while being developed. The black resin film falls off because the black resin film at its surface portions absorbs light during patterning by photolithography and thus fails to be sensitized inside. Although improvement is possible to a certain extent if the black resin film is formed as a thin film, this solution leads to a new problem of lowered optical density. As an optical density, an OD value of 3.0 or higher is said to be necessary. Further, in an effort to increase an optical density, an increased carbon content results in a trade off in that a ratio of an acrylic component, which contributes to a tight contact with the underlying member, decreases and hence a contact capability decreases. In short, such stripping of the black resin film becomes particularly remarkable when the black matrix 113 is formed thick or the carbon content in the black matrix 113 is increased and the like. This is another problem in that it is difficult to enhance optical density, namely, light shielding capability for the purpose of obtaining excellent contrast. In contrast, in the case of a color filter, since light is transmitted even inside, sufficient sensitizing is possible.
Further, a color liquid crystal display panel which uses a laminated member of three color layers as a light shielding film has been proposed (Japanese Patent Laid-Open Publication No. Sho 62-250416). However, even if such a laminated member is used on a TFT-side glass substrate as an alternative to a black matrix, sufficient shielding of light is not achieved, and therefore, the OD value decreases and contrast accordingly decreases.
On the other hand, as such a color filter for liquid crystal display in which three color layers are formed on a counter glass substrate described earlier, a color filter in which adjacent color layers are overlapped at their boundaries has been proposed (Japanese Patent Laid-Open Publication No Sho 63-173023). In the case of the color filter described in this official gazette, black ink is applied using a roller to the overlap portions described above to thereby form the black matrix. However, in such a color filter, since a light shielding rate becomes different depending on the color of the adjacent color layer, the contrast of a displayed image varies, and hence, the image appears uneven.
According to the present invention, a color liquid crystal display panel comprises first and second transparent substrates which are arranged to face each other, a liquid crystal layer provided between the first and the second transparent substrates, a plurality of thin film transistors provided on the first transparent substrate, an insulation film provided on the first transparent substrate so as to cover the thin film transistors, a color filter which comprises first to third color layers stacked on the insulation film, a contacting color layer which is provided on the insulation film in a region above the thin film transistors and comprises at least one color layer selected from the group consisting of the first to third color layers, and a black matrix which is provided on the contacting color layer and has opening portions for transmitting light from the color filter.
According to the present invention, a contacting color layer including at least one color layer selected from the group consisting of the first to third color layers is provided between the black matrix and the insulation film. As to the color layers, since light even passes through the inside of the color layers during fabrication of the color layers by photolithography, the color layer is sufficiently sensitized, and therefore, contact between the color layer and the insulation film is tight. As to the black matrix, high optical density is obtained since at least one of the color layers is disposed under the black matrix, and therefore, the black matrix can be formed to be thin. Moreover, since the base materials of the black matrix and the color layers are usually the same, e.g., an acrylic resin, contact between the color layers and the black matrix is also high. As a result, tight contact between the black matrix and the insulation film is achieved. Since this suppresses peeling of the black resin film, which serves as the raw material of the black matrix, fine patterning is possible during development, and high fineness is accordingly realized. In addition, since the color layers disposed under the black matrix as well serve as a light shielding layer in addition to the black matrix, high optical density is obtained.